Abstract: A method for producing a round tube from a ceramic material or a glass-ceramic material or mixtures thereof is described. The method comprises introducing a silicate-ceramic, oxide-ceramic and/or non-oxide-ceramic material-forming agent into a melting vessel, which has along a longitudinal axis a tubular wall which defines a tubular cavity, wherein the melting vessel rotates about its longitudinal axis. A uniform layer of the ceramic and/or glass-ceramic material-forming agents is thereby formed, lying on the inner side of the wall, by means of centrifugal forces generated by rotation and is heated by means of a heat source arranged in the inner cavity of the melting vessel until at least the inner side of the layer of material-forming agents has melted. Such tubes can be used for various industrial purposes.

Abstract: The method of evaluating an optical defect in a transparent material includes irradiating the material with light to produce scattered light from the defect, rotating the material about a rotation axis passing through the defect, measuring scattered light intensity at a scattering angle (?s) to the rotation axis by means of a detector, determining the dependence of the measured scattered light intensity on rotation angle (?s) around the rotation axis and characterizing size and/or shape of the defect from that dependence. The apparatus for performing the method has a light source, a rotatable holder for the transparent material, a light sensitive receiving device and an imaging optical system for imaging scattered light from the material within a certain angular range on a detector surface of the receiving device.

Abstract: The process of making synthetic silica glass occurs in a combustion chamber of a muffle furnace. It includes producing a gas flow containing a fuel, an oxidizer, and a silicon compound that is converted by flame hydrolysis and/or by chemical oxidation to SiO2 particles, and depositing them on a target to form a roll-shaped silica glass body. The combustion chamber is provided with a gas inlet and a gas outlet arranged at opposite ends of the combustion chamber, which widens from the inlet to the outlet. The gas flow is produced by a central nozzle for the silicon compound, a first concentric ring-shaped nozzle for the oxidizer, and a second concentric ring-shaped nozzle for the fuel. The process is characterized by a ratio of areas of ring gaps of the ring-shaped nozzles of from 1:4 to 1:6.1. The apparatus for the process is also part of the invention.

Abstract: Single crystals with low scattering, small refractive index differences and few small angle grain boundaries have a bi-directional scattering distribution function value (BSDF) of less than 1.5*10?6 or 5*10?7.

Abstract: The method provides CaF2 single crystals with low scattering, small refractive index differences and few small angle grain boundaries, which can be tempered at elevated temperatures. In the method a CaF2 starting material is heat-treated for at least five hours at temperatures between 1000° C. and 1250° C. and then vaporized at a temperature of at least 1100° C. in a vacuum of at most 5*10?4 mbar to form a vapor. The vapor is condensed at a temperature between 500° C. to 1280° C. to form a condensate. Then a melt formed from the condensate is cooled in a controlled manner to obtain the single crystal, which is subsequently tempered. The method is preferably performed with a CaF2 starting material including waste material and cuttings from previously used melts.

Abstract: The method provides CaF2 single crystals with low scattering, small refractive index differences and few small angle grain boundaries, which can be tempered at elevated temperatures. In the method a CaF2 starting material is heat-treated for at least five hours at temperatures between 1000° C. and 1250° C. and then sublimed at a sublimation temperature of at least 1100° C. in a vacuum of at most 5*10?4 mbar to form a vapor. The vapor is condensed at a condensation temperature of at least 500° C., which is at least 20° C. below the sublimitation temperature, to form a condensate. Then a melt formed from the condensate is cooled in a controlled manner to obtain the single crystal, which is subsequently tempered. The method is preferably performed with a CaF2 starting material including waste material and cuttings from previously used melts.

Abstract: The method provides CaF2 single crystals with low scattering, small refractive index differences and few small angle grain boundaries, which can be tempered at elevated temperatures. In the method a CaF2 starting material is heat-treated for at least five hours at temperatures between 1000° C. and 1250° C. and then vaporized at a temperature of at least 1100° C. in a vacuum of at most 5*10?4 mbar to form a vapor. The vapor is condensed at a temperature between 500° C. to 1280° C. to form a condensate. Then a melt formed from the condensate is cooled in a controlled manner to obtain the single crystal, which is subsequently tempered. The method is preferably performed with a CaF2 starting material including waste material and cuttings from previously used melts.

Abstract: For improving the refractive index homogeneity of quartz glass bodies, at least one burner is disposed movably in a melting device with respect to the quartz glass object which is to be produced. The burner has three essentially concentrically disposed groups of nozzles for metering the raw material, supplying the hydrogen and supplying the oxygen. Corresponding to the changes in the distribution of OH and H2 between the center and the edge of the quartz glass object, the volumes of hydrogen and/or oxygen of the burner gases flowing change as a function of the burner position with respect to the quartz glass object in order to bury the mixing ratio in the burner gas.